It is estimated that 50% of the 20 million people in the western world with tattoos are interested in having the tattoos removed. Methods of tattoo removal have been developed, but those methods are often ineffective, take a long period of time, and involve considerable pain.
Professional tattoos are created by injecting tattoo inks with a rapidly reciprocating needle that drives ink particles into the dermis to a depth of 0.6 mm to 2.2 mm. The inks used in tattooing are derived from exogenous pigments, most of unknown purity. Pigments in tattoo ink include iron oxides, chromium oxide, aluminum oxide, titanium oxide, barium sulfate, zinc oxide, sodium copper silicate, sodium aluminum silicate, copper carbonate, dioxazine and carbazole. Following injection, the ink pigment particles reside in the interstitial space between dermal cells where they form large aggregates of about 140 μm to 180 μm until fibroblasts or macrophages engulf the pigment particles and internalize the tattoo ink into the skin cells. The size of the ink particle aggregates and the collagen network surrounding the aggregates help keep the ink pigments within the skin making the tattoo permanent, thus the difficulty with removal of tattoos.
The most popular method for removing unwanted tattoos is the laser method, which delivers short pulses of intense light that pass through the epidermis to be selectively absorbed by the tattoo pigment in the dermis. The lasers developed specifically for use in tattoo removal use a technique known as Q-switching, which refers to the laser's short, high-energy pulses. The lasers typically used are a Q-switched frequency doubled Nd:YAG laser (532 nm) for red orange and purple pigment; a Q-switched Nd:YAG laser (1064 nm) for black pigment; a Q-switched ruby laser (694 nm) for black pigment; and a Q-switched alexandrite laser (755 nm) for blue and green pigment.
The mechanism by which Q-switched lasers remove tattoos involves selective rupture of the skin cells, breakdown of tattoo ink particle aggregates, and ink removal by trans-epidermal elimination and/or lymphatic transport (Taylor et al., J. Invest. Dermatol., 97:131-136 (1991); Ferguson et al., Br. J. Dermatol., 137:405-410 (1997)). Although the human immune system is able to remove some of the pigment fragments, causing fading of the tattoo (Wheeland, Lasers in Surgery and Medicine 16:2 23 (1995); Zelickson et al., Lasers in Surgery and Medicine 15:364 372 (1994)), most pigment fragments become re-phagocytosed by still intact dermal cells and so the tattoo remains visible (Ferguson et al., British Journal of Dermatology 137:405 410 (1997)).
Laser treatments must be spaced at least one month apart because the laser causes a painful burn to form on the skin. Laser treatments may not completely remove a mature tattoo, and are expensive, time consuming, and painful.